Clinical chemistry investigations with biological fluids have been substantially simplified in recent years by the development of the so-called "dry chemistry". Thus, for example, the development of test strips or devices for determination of glucose in whole blood provided the possibility of diabetics carrying out a check on their blood sugar level by themselves. Indeed, this check has already become an important component of the therapy of diabetics. Moreover, the use of test strips is not limited only to the determination of glucose. Test strips for enzymatic determinations, substrates, such as, for example, cholesterol or triglycerides, or ions or for drug monitoring are not well known.
Many examples of so-called "dry chemical" determination systems, also called test strips, are described in the literature. The reagents necessary for such test strips normally are contained in a carrier matrix. The sample containing the analysis substance is applied to the test strip. The sample material, blood, serum, urine or another biological fluid, can be applied diluted or undiluted. A reaction which generates a detectable signal (for example coloration or fluorescence) which is proportional to the concentration of the analysis substance then takes place in the test strip.
Many materials are known to be suitable as the carrier matrix, such as, for example, paper, plastics, gelatin or cellulose derivatives.
In the production of test strips, it is frequently necessary for hydrophobic substances also to be introduced into the carrier matrix.
It is known that one possibility for introducing hydrophobic substances into the carrier matrix is by impregnation of the matrix with an organic solution of the substances. In this type of production, however, two or even more impregnating and drying steps are usually necessary, since hydrophilic substances which are soluble in aqueous systems frequently also have to be introduced into the matrix. Another possibility is to prepare emulsions of the substances. This requires a large amount of energy, however, to achieve a sufficiently fine distribution of the substances.
Surprisingly, it has now been found that aqueous dispersions of hydrophobic reagents can be prepared by a very simple process using ionomeric polymers. These dispersions have an excellent stability and small particle size. They can, therefore, be very readily used in the preparation of reagent layers.